Fuel divider and ecology system for a gas turbine engine

ABSTRACT

A fuel control system for supplying metered quantities of fuel from a fuel supply ( 11 ), through a fuel pump ( 13 ), a metering valve ( 15 ) and a pressurizing valve ( 17 ) to a plurality of engine fuel manifolds ( 31   a   , 31   b   , 33 ) includes an ecology valve ( 43 ) for withdrawing fuel from the engine fuel manifolds ( 31   a   , 31   b   , 33 ) during cessation of engine operation and for returning fuel to the engine fuel manifolds ( 31   a   , 31   b   , 33 ) to be burned during normal engine operation. The ecology valve ( 43 ) includes a valve housing ( 44 ) having a plurality of ecology ports ( 50, 52, 54 ) adapted to be coupled to corresponding ones of the engine fuel manifolds ( 31   a   , 31   b   , 33 ) and a control port ( 46 ) adapted to be connected to a corresponding control port ( 45 ) of the fuel pressurizing valve ( 17 ). A movable piston ( 63 ) is supported within the valve housing ( 44 ) for reciprocable motion and divides the interior of the valve housing ( 44 ) into a variable volume control chamber ( 71 ) coupled to the control port ( 46 ) and a variable volume fuel reservoir ( 55 ) which is selectively coupled to and uncoupled from the ecology ports ( 50, 52, 54 ) by the piston ( 63 ). Fuel is withdrawn from the manifolds ( 31   a   , 31   b   , 33 ) seriatim. A fuel flow dividing arrangement is located intermediate the pressurizing valve ( 17 ) and the engine fuel manifolds ( 31   a   , 31   b   , 33 ) for distributing appropriately fuel flow among the manifolds and includes a concatenated pair of two-way splitter valves ( 39, 41 ) comprising a first splitter valve ( 39 ) distributing the fuel flow between an atomizer nozzle manifold ( 31   b ) and the remaining manifolds ( 31   a   , 33 ), and a second splitter valve ( 41 ) distributing down stream fuel flow from the first splitter valve ( 39 ) between upper and lower manifolds ( 31, 33 ).

[0001] The present invention relates generally to fuel delivery systemsfor engines, especially aircraft gas turbine engines, and moreparticularly to ecology and fuel flow splitting functions for such fueldelivery systems.

[0002] Some fuel delivery systems for gas turbine engines requiremultiple fuel manifolds to segregate various types of fuel nozzles foroptimal engine performance. A means of dividing this flow between themanifolds is therefor required. U.S. Pat. No. 5,809,771 Wernbergdiscloses an ecology valve and a fuel flow splitting valve having asingle piston operable in two different regions, one for modulating flowto primary and secondary engine nozzles as a function of fuel pressureand another where flow to primary and secondary engine nozzles isdetermined by the fixed port geometry. It is very difficult to extendthis concept to more than two distinct engine manifolds.

[0003] Some engines also require an ecology function that removes a setquantity of fuel from the engine fuel manifold(s) upon cessation ofengine operation. Fuel removal is required for two reasons. First, itkeeps fuel from vaporizing into the atmosphere. Second, it keeps fuelfrom coking on the engine's fuel nozzles, a condition that hindersnozzle performance. Prior art ecology systems have used an arrangementof pistons, check valves, plumbing, reservoirs and pumps to accomplishthis task. In engines requiring multiple fuel manifolds, multipleecology valves or a multiple chambered ecology valve have been used.These types of architecture result in complex, high cost and weightecology systems. A two chambered valve is disclosed in theabove-mentioned Wernberg U.S. Pat. No. 5,809,771. In the Wernbergsystem, fuel is simultaneously withdrawn from the two manifolds and aseparate chamber is required for each engine manifold to ensure discretefuel removal from those manifolds upon engine shut-down. It is also verydifficult to extend this concept to more than two distinct enginemanifolds. The Wernberg system employs at least one check valvedownstream of the ecology valve for diverting a part of the modulatedflow from the primary to the secondary manifold. Such downstream valvingallows a degree of undesirable cross-talk between the manifold supplylines and may reduce engine fuel flow reliability or increase the loadon the fuel supply pump.

[0004] It is desirable to minimize the fuel remaining in an engine fuelmanifold upon cessation of engine operation and to provide a compact,economical ecology function for fuel supply systems. It is alsodesirable to achieve such an ecology function by employing a simplesingle diameter piston valve which is controlled solely by a signal froma pressurizing valve, and to accomplish the ecology function whileavoiding any cross-talk between the several manifold fuel supply linesthereby maintaining the fuel pressure integrity in those several lines.It is further desirable to avoid this cross-talk while achieving a fuelsplitting function which is operable to appropriately distribute fuel toa plurality of engine fuel manifolds.

[0005] The present invention provides solutions to the above problems inthe form of a fuel divider and ecology system adapted for an enginerequiring three discrete fuel manifolds. One manifold contains atomizernozzles (for engine start), and two manifolds contain air blast nozzles,one servicing the lower half and the other servicing the upper half ofthe engine. For the flow dividing function, the system incorporates aplurality of valves to appropriately distribute metered burn flow tothese three fuel manifolds. This system accomplishes the ecologyfunction using one single chamber staged valve, and modifying the mainfuel control pressurizing valve to include a pressure switchingfunction. This approach limits the ecology components to one ecologyvalve piston, and one plumbed line from the pressurizing valve tocontrol it. The fuel splitting function is achieved by a first splittervalve which divides the fuel flow from a pressurizing valve betweenatomizer or start-up nozzles and air blast or main running nozzles; anda second splitter valve which subdivides flow between the upper andlower manifolds.

[0006] In accordance with one form the invention, an ecology valve forminimizing the accumulation of fuel in a multiple fuel manifold enginesystem when the engine is shut down has a control port coupled to andcontrolled solely by an engine fuel system pressurizing valve and ahousing with a piston reciprocable therein between first and secondextreme positions. The piston defines, in conjunction with the housing,a variable volume chamber for sequentially withdrawing fuel from each ofthe engine fuel manifolds when the engine is de-energized and the pistonmoves from the first extreme position toward the second extreme positionthereby purging the manifolds of fuel. There is a spring within thehousing which supplies a force to the piston to urge the piston towardthe second extreme position and the piston responds to high pressure atthe ecology valve control port overpowering the spring to move towardthe first extreme position. There are a plurality of sidewall or ecologyports in the housing selectively opened and closed by piston movement tocouple the variable volume chamber and selected fuel manifolds.

[0007] In accordance with another form of the invention, an improvedfuel flow dividing arrangement is located intermediate a pressurizingvalve and a plurality of engine fuel manifolds for appropriatelydistributing fuel flow among the manifolds. The arrangement includes aconcatenated pair of two-way splitter valves one of which distributesfuel flow between an atomizer nozzle manifold and the remainingmanifolds. Another splitter valve distributes the down stream fuel flowfrom the first splitter valve between upper and lower air blast nozzlemanifolds. The second splitter valve provides a pair of low volume fuelflow paths to the upper and lower manifolds during engine start-up and asecond pair of high volume fuel flow paths to the upper and lowermanifolds during normal engine running conditions. There is a headeffect fuel flow restricting valve in the low volume fuel flow path tothe lower manifold to compensate for elevation difference induced lowburn rate fuel flow differences between the upper and lower manifolds.The first splitter valve provides a low volume fuel flow path to thesecond splitter valve during engine start-up and a second high volumefuel flow path to the second splitter valve during normal engine runningconditions, and switches fuel routed to the atomizer nozzles frompressurizing valve discharge pressure to the lower manifold pressure.

BRIEF DESCRIPTION OF THE DRAWING

[0008]FIG. 1 is a schematic representation of an illustrative aircraftfuel system including an ecology function according to the presentinvention;

[0009]FIG. 2 is a detailed cross-sectional view of the pressurizingvalve, and flow divider and ecology module of FIG. 1 in the engine offposition;

[0010]FIG. 3 is a cross-sectional view similar to FIG. 2, andillustrating the pressurizing valve beginning to open prior to enginestart-up and commencement of fuel discharge from the ecology valve;

[0011]FIG. 4 is a cross-sectional view similar to FIGS. 2 and 3, andillustrating a second stage of fuel discharge from the ecology valve;

[0012]FIG. 5 is a cross-sectional view similar to FIGS. 2-4, andillustrating a third stage of fuel discharge from the ecology valve;

[0013]FIG. 6 is a cross-sectional view similar to FIGS. 2-5, andillustrating start-up conditions for the splitter valves;

[0014]FIG. 7 is a cross-sectional view similar to FIGS. 2-6, andillustrating the flow divider and ecology module in the normal enginerun configuration; and

[0015]FIG. 8 is a cross-sectional view similar to FIGS. 2-7 butillustrating an alternative embodiment of the head effect valve of theflow divider and ecology module during normal engine run configuration.

[0016] Corresponding reference characters indicate corresponding partsthroughout the several views of the drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0017] The following abbreviations are used for various pressuresthroughout the description: PIN fuel control inlet pressure POF pumpinterstage pressure before filter PO pump interstage pressure afterfilter P1 high pressure pump discharge P2 metering valve dischargepressure P3 pressurizing valve discharge pressure PAT burn flow pressureto atomizer nozzles PAB burn flow pressure to air blast nozzles PABLburn flow pressure to lower air blast nozzles PABU burn flow pressure toupper air blast nozzles PXE ecology valve control pressure

[0018]FIG. 1 is a block diagram showing a gas turbine engine fueldivider and ecology module, as well as the related upstream and downstream fuel system components. In FIG. 1, an illustrative aircraft fuelsupply system includes a supply tank 11 from which fuel is fed to boostpump 13 and a filter 21 to a high pressure pump 14. The high pressurepump 14 discharge pressure P1 is supplied to a variable orifice meteringvalve 1 5 and through a pressurizing valve 17 and a flow divider andecology module 19 to an engine. The pressurizing valve 17 maintains areference pressure level P2 on the downstream side 24 of the meteringvalve 15 and the bypass valve 23 selectively diverts fuel from line 25back through line 27 to the high pressure pump 14 inlet to maintain aconstant head or pressure drop across the metering valve 15. Fuelentering the fuel manifolds 31 and 33 of the engine from pressurizingvalve 17 flows through line 37, a first flow dividing valve 39 and asecond flow dividing valve 41. Fuel entering the atomizer nozzles infuel manifolds 31 from pressurizing valve 17 flows directly from thefirst flow divider valve 39 to the engine manifold. The pressurizingvalve 17 opens when burn flow pressure is sufficiently greater thanreturn flow pressure, that is, when the pressure differential between P2on line 24 and PO on line 51 becomes sufficiently great and closes whenthat pressure differential drops below a certain threshold. Thepressurizing valve 17 includes appropriate lands and grooves to coupleselectively the staged ecology valve 43, by means of control line orport 45, to either fuel control inlet pressure on line 47 or to meteringvalve 1 5 discharge pressure by way of line 24. The components of theflow divider and ecology module 19 are shown in greater detail in FIGS.2-7.

[0019] In FIGS. 2-7, the ecology valve 43 includes a valve housing 44including ecology ports 50, 52 and 54 which are coupled to the enginefuel manifolds 31 and 33. The ecology valve also includes a control port46 connected to a corresponding control port of the fuel pressurizingvalve 17. There is a movable piston 63 supported within the valvehousing 44 for reciprocable motion along an axis. The piston 63 dividesthe valve housing into a variable volume control chamber 71 (see FIG. 3)which is coupled to the control port 46 and a variable volume fuelreservoir 55. The piston 63 has one extreme position (FIGS. 5, 6 and 7)in which a sidewall port 64 is open to a first port 54 to couple thefuel reservoir 55 to a first or upper engine fuel manifold 33 while theremaining ports 52 and 50 are closed isolating the reservoir from thelower engine fuel manifold 31 which comprises air blast manifold 31 aand atomizer manifold 31 b. The piston 63 has a second extreme position(FIG. 2) in which a second port 50 is open to couple the fuel reservoir55 to the hybrid nozzles of the atomizer manifold 31 b of the second orlower engine fuel manifolds 31 while the other ports 52 and 54 areclosed isolating the reservoir from air blast manifold 31 a of lowermanifolds 31 and from the remaining engine fuel upper manifold 33. In apreferred form, there are exactly three ports selectively opened andclosed by piston motion with the port 52 opening to couple the fuelreservoir to engine fuel lower manifolds 31 only while the piston is intransition and closing both of the other ports 50 and 54 as in thetransition from FIG. 3 to FIG. 4. Thus, the piston 63 has one extremeposition (FIGS. 5-7) in which it closes at least one port such as 50 anda second extreme position (FIG. 2) in which it closes at least one otherport 54. Fuel is withdrawn sequentially from the manifolds 33, 31 a and31 b. There are three manifolds (31 a, 31 b and 33) and three disjointtime intervals, one for each manifold, during which fuel is withdrawnfrom or supplied to exactly one manifold. Both withdrawing from andsupplying fuel to any one manifold is substantially completed before thewithdrawal from or supplying to another manifold commences.

[0020]FIG. 2 shows the pressurizing valve 17 closed, blocking the P2/P3flow path, with its switching function connecting PXE pressure on line45 (FIG. 1) to PIN pressure on line 47 by way of the groove 59 in piston57. As illustrated in FIG. 2, this low pressure PIN at the ecology valvecontrol port 46 exerts a force on the piston 63 which is less than theforce exerted by spring 48 to urge the piston 63 toward its uppermostposition as illustrated, a condition indicative of a quiescent enginecondition. The ecology valve 43 is thereby shown filled with fuel andthe engine manifolds are purged. Set amounts of fuel have been retractedfrom the manifolds into the spring cavity 55 of the valve. The flowdivider valves 39 and 41, and head effect valve 53 are also in theirclosed positions. These are the engine off positions of all valves.

[0021]FIG. 3 shows the piston 57 of pressurizing valve 17 at the P2/P3near open or cracking position, with its switching function connectingPXE pressure in line 45 to P2 pressure in passage 49 via groove 61. Atthis position with the P2/P3 flow path blocked, fuel controlpressurization is up, and manifold pressure (as well as the spring sideof the ecology valve) is down. The piston 63 of ecology valve 43 isshown traveling toward its energized position, staging the return ofstored fuel from chamber 55 on the spring side of the valve to themanifolds. At this ecology valve stage, fuel has been returned fromchamber 55 to the atomizer manifold 31 b (PAT pressure) by way of line65. This process is occurring during engine spool up (prior to start).

[0022]FIG. 4 shows the second stage position of the ecology valve 43,where fuel has been returned by way of conduit 67 to the lower air blastfuel manifolds 31 (PABL pressure). The pressurizing valve 17 and flowdivider valves 39 and 41 remain in the same functional positions asdescribed in FIG. 3.

[0023]FIG. 5 shows the final position (last stage) of the ecology valve43, where fuel has been returned to the upper air blast fuel manifold 33(PABU pressure) through conduit 69. The pressurizing valve 17 and flowdivider valves 39 and 41 remain in the same functional positions asdescribed in FIGS. 3 and 4 up to the time that the ecology valve 43reaches its hard stop, fully energized position with the chamber 71 (atpressure PXE) at its maximum volume. It should be noted that all threemanifolds 31 a, 31 b and 33 have been refilled by the volume of fuelexpelled from the ecology valve chamber 55.

[0024] IS Comparing FIGS. 2-5 it will be noted that the piston 63 hasthe single sidewall port 64 which sequentially communicates with housing44 sidewall ports 50, 52 and 54. Thus, the ecology valve 43 has a firstsidewall port 50 which is closed by the piston 63 when the piston is inits lowermost (FIG. 5) extreme position, a second sidewall port 52 whichis closed by the piston 63 when the piston is in lowermost (FIG. 5) aswell as its uppermost (FIG. 2) extreme positions, and a third sidewallport 54 which is closed by the piston 63 when the piston is in itsuppermost extreme position. The second or middle sidewall port 52 opensduring piston movement between its extreme positions to couple thevariable volume chamber 55 with engine fuel lower manifolds 31. Whilethere may be piston positions such as illustrated in FIG. 4 where theport 64 momentarily communicates with two sidewall ports, 52 and 54 forexample, in substantially all piston positions, the piston closes atleast two sidewall ports. All three ports are never open simultaneously.

[0025]FIG. 6 shows the pressurizing valve 17 opened, allowing meteredfuel flow to pass to the flow divider and ecology module 19 (FDEM)through conduit 37. As flow enters the FDEM 19, the piston 75 ofatomizer/air blast flow divider valve 39 translates off its soft seat74, allowing fuel to flow to the atomizer manifold 31 b at PAT pressurethrough line 73 and restricted flow to pass through port 83 and line 42to the upper/lower air blast manifold flow divider valve 41 (PABpressure) via sequential side wall orifices 77 and 78 in piston 75. Thepiston 79 of upper/lower air blast manifold flow divider valve 41translates from its closed position, allowing flow to the upper manifold33 through conduits 81 and 69 at PABU pressure. The translation ofpiston 79 also allows a biased flow of fuel to the lower manifold 31(PABL pressure) through head effect valve 53 and line 67. The PABLpressure flow is biased by the head effect valve 53 which compensatesfor differences in elevation and line loss between the upper and lowermanifolds. Without this compensation, the lower manifolds 31 a and 31 bwould flow more fuel Is than the upper manifold 33, particularly at lowmetered burn flow rates. FIG. 6 illustrates the approximate positions ofthe valves during an engine start up.

[0026]FIG. 7 shows the conditions defined in FIG. 6, but with a higherrate of burn flow. As flow increases, the pressurizing valve 1 7 furtheropens allowing additional metered fuel flow to the FDEM 19 through line37. The piston 75 of atomizer/air blast flow divider valve 39 furthertranslates from its closed position, opening port 83 that allowsadditional fuel flow to pass to the upper/lower air blast manifold flowdivider valve 41 (PAB pressure) to increase the flow that was previouslythrough side wall orifices 77 and 78 in piston 75. The side wallorifices 77 and 78 are staged so that when orifice 77 is closing, thesecond orifice 78 opens, keeping the orifice area and flow fromdiminishing. At this position of valve 75, fuel routed to thecombination atomizer and air blast nozzles (hybrid nozzles) of atomizermanifold 31 b is supplied from the lower manifold pressure (PABL) vialines 76 and 73 and valve 39 opening 80, rather than from pressurizingvalve 17 discharge pressure P3. The purpose for providing lower airblast manifold pressure (PABL) to the atomizer manifold 31 b is toequate the total flow of a hybrid nozzle in manifold 31 b to that of theflow of an air blast nozzle in the air blast manifold 31 a (see FIG. 1).The piston 79 of upper/lower air blast manifold flow divider valve 41further translates from its closed position, opening ports 85 that allowadditional fuel flow to the upper (PABU pressure) manifold 33 and thelower (PABL pressure) manifolds 31, while maintaining equal flow tothese manifolds.

[0027] Comparing FIGS. 6 and 7, the splitter valve 39 provides a lowvolume fuel flow path by way of side wall orifices 77 and 78 to thesplitter valve 41 during engine start-up and a second high volume fuelflow path via port 83 (in parallel and in addition to the first) to thesplitter valve 41 during normal engine running conditions. As also seencomparing FIGS. 6 and 7, the splitter valve 41 provides a pair of lowvolume fuel flow paths by way of passage 81 and head effect valve 53 tothe upper manifold 33 and lower manifolds 31 respectively during enginestart-up and a second pair of high volume fuel flow paths 69 and 67 tothe upper manifold 33 and the lower manifolds 31 respectively duringnormal engine running conditions. The head effect fuel flow restrictingvalve 53 is in the low volume fuel flow path to the manifolds 31 tocompensate for elevation difference, induced low burn rate fuel flowdifferences between the upper and lower manifolds. FIG. 7 illustratesthe approximate positions of the valves for an engine run condition. Itshould be noted that during all engine operating conditions (FIGS. 6 and7), the piston 63 of the ecology valve 43 is in its full energizedposition against that respective hard stop, making the ecology valve 19a non-dynamic feature with respect to metered burn flow to the engine.

[0028] The process of cycling an engine from an engine-off condition,through start-up and substantially full throttle run, and subsequentshut-down and back to the engine-off condition should now be clear. Whenthe pilot or other operator issues a command to start the engine, P2pressure is supplied by way of line 45 to expand chamber 71 anddischarging a quantity of fuel from the ecology reservoir 55 by way ofport 50 into manifold 31 b. Additional motion of piston 63 expels fuelinto the other two manifolds 31 a, 33 from reservoir 55. Additional fuelis supplied to manifold 31 b and a limited quantity of additional fuelfrom fuel source 11 is supplied to the manifolds 31 a and 33 to startthe engine. The supply of fuel to all manifolds is increased to bringthe engine to substantially full throttle operation. Later, the pilot orother operator issues a shut-down command interrupting fuel flow to allthe manifolds to initiate engine shut-down. Lines 45 and 47 arereconnected by the pressurizing valve 17 and piston 63 moves upwardunder the urging of spring 48 sequentially extracting fuel from themanifolds and storing the extracted fuel in the ecology reservoir 55 tobe burned during a subsequent engine start-up.

[0029]FIG. 8 illustrates the aircraft fuel system of FIG. 7 but includesan alternative embodiment for the head effect valve 53 wherein weight orload member 92 and pressure loaded pin 91 are used to urge ball or valvemember 93 against its seat. During normal engine run conditions, PAT andPABL pressures in lines 73 and 67 become equal as also shown in FIG. 7,with no pressure differential existing across the pin 91. In thiscondition, the ball 93 is urged against its seat solely by the forceexerted by the combined weight of the pin 91 and weight 92, compensatingonly for head effect and line losses. During engine start-up conditionsas illustrated in FIG. 6, PAT pressure in line 73 a and its associatedorifice (see FIG. 8) and which is exerted on the end of the pin 91 isgreater than PABL pressure on the other end of the pin, which createsadditional force to urge the ball valve 93 against its seat. Thisfurther throttles or lessens fuel flow being delivered to the lowermanifold air blast nozzles via line 67, which compensates for thegreater flow being delivered to the lower manifold atomizer nozzles vialine 73 during engine start-up. This results in equal flow to the upperand lower halves of the engine for all conditions, including enginestart-up. It should be noted that the weight 92 shown in the head effectvalve 90 of FIG. 8 could be replaced with a spring as shown in FIGS.2-7, and the spring or weight shown in FIGS. 2-8 could be replaced byany other equivalent device or structure that provides an appropriateload upon the ball valve.

What is claimed is:
 1. A fuel control system for supplying metered quantities of fuel from a fuel supply, through a fuel pump, a metering valve and a pressurizing valve to a plurality of engine fuel manifolds, the improvement comprising: an ecology valve having a control port coupled to and controlled solely by the pressurizing valve, the ecology valve including a housing and a piston disposed therein and movable between first and second extreme positions, the piston defining, in conjunction with the housing, a variable volume chamber for sequentially withdrawing fuel from each of the engine fuel manifolds when the engine is de-energized and the piston moves from the first extreme position toward the second extreme position thereby purging the manifolds of fuel.
 2. The improvement of claim 1, further comprising spring means within the housing engaging and applying a force to the piston to urge the piston toward said second extreme position, the piston responding to high pressure at the ecology valve control port and the force of the pressure exceeding said spring force to move toward said first extreme position and to lower pressure at the ecology valve control port, the force of the lower pressure on the piston being less than said spring force and the lower pressure being indicative of cessation of engine operation, to move toward said second extreme position.
 3. The improvement of claim 1, further including a plurality of sidewall ports in the housing for selectively coupling the variable volume chamber and selected fuel manifolds and including a first sidewall port which is closed by the piston when the piston is in said first extreme position, a second sidewall port which is closed by the piston when the piston is in said first extreme position and closed by the piston when the piston is in said second extreme position, and a third sidewall port which is closed by the piston when the piston is in said second extreme position; the second sidewall port opening during piston movement from one extreme position to the other extreme position to couple the variable volume chamber with one engine fuel manifold.
 4. The improvement of claim 3, wherein at substantially all piston positions, the piston closes at least two sidewall ports.
 5. The improvement of claim 1, further including fuel flow dividing means intermediate the pressurizing valve and the engine fuel manifolds for appropriately distributing fuel flow among the plurality of engine fuel manifolds.
 6. The improvement of claim 5, wherein the engine fuel manifolds include an atomizer nozzle manifold, an upper air blast nozzle manifold and a lower air blast nozzle manifold and the fuel flow dividing means includes a concatenated pair of two-way splitter valves, a first splitter valve distributing the fuel flow between the atomizer nozzle manifold and the remaining manifolds, and a second splitter valve down stream from the first splitter valve and distributing fuel flow between the upper and lower air blast nozzle manifolds.
 7. The improvement of claim 6, wherein the second splitter valve provides a pair of low volume fuel flow paths to the upper and lower manifolds during engine start-up and a second pair of high volume fuel flow paths to the upper and lower manifolds during engine running conditions.
 8. The improvement of claim 7, further comprising a fuel flow restricting head effect valve in the low volume fuel flow path to the lower manifolds to compensate for low burn rate fuel flow differences between the upper and lower air blast nozzle manifolds.
 9. The improvement of claim 8, wherein the head effect valve reduces fuel flow to the air blast nozzles of the lower air blast nozzle manifold in order to compensate for greater fuel flow to the atomizer nozzle manifold during engine start-up conditions.
 10. The improvement of claim 9, wherein the combined fuel flow of the atomizer nozzle manifold and lower air blast nozzle manifold substantially equals that of the upper air blast nozzle manifold.
 11. The improvement of claim 10, wherein the head effect valve communicates with both fuel pressure being supplied to the atomizer nozzle manifold and fuel pressure being supplied to the lower air blast nozzle manifold.
 12. The improvement of claim 11, wherein the head effect valve includes a valve member, a load member, and a pin.
 13. The improvement of claim 6, wherein the first splitter valve provides a low volume fuel flow path to the second splitter valve during engine start-up and a second high volume fuel flow path to the second splitter valve during engine running conditions.
 14. The improvement of claim 13, wherein the first splitter valve provides an increased rate of fuel flow to the atomizer nozzle manifold during engine start-up.
 15. The improvement of claim 14, wherein the first splitter valve provides a different rate of fuel flow to the atomizer nozzle manifold during engine running conditions so that the different rate of fuel flow to nozzles of the atomizer nozzle manifold is substantially equal to the rate of fuel flow to an air blast nozzle in the lower air blast nozzle manifold.
 16. A fuel control system for supplying metered quantities of fuel from a fuel supply, through a fuel pump, a metering valve and a pressurizing valve to a plurality of engine fuel manifolds including an atomizer nozzle manifold, an upper air blast nozzle manifold and a lower air blast nozzle manifold, an improved fuel flow dividing arrangement intermediate the pressurizing valve and the engine fuel manifolds for appropriately distributing fuel flow among the plurality of engine fuel manifolds comprising: a concatenated pair of two-way splitter valves comprising a first splitter valve distributing the fuel flow between the atomizer nozzle manifold and the remaining air blast manifolds, and a second splitter valve distributing the down stream fuel flow from the first splitter valve between the upper and lower nozzle manifolds.
 17. The improvement of claim 16, wherein the second splitter valve provides a pair of low volume fuel flow paths to the upper and lower manifolds during engine start-up and a second pair of high volume fuel flow paths to the upper and lower manifolds during normal engine running conditions.
 18. The improvement of claim 17, further comprising a fuel flow restricting head effect valve in the low volume fuel flow path to the lower manifolds to compensate for low burn rate fuel flow differences between the upper and lower air blast nozzle manifolds.
 19. The improvement of claim 18, wherein the head effect valve reduces fuel flow to the air blast nozzles of the lower air blast nozzle manifold in order to compensate for greater fuel flow to the atomizer nozzle manifold during engine start-up conditions.
 20. The improvement of claim 19, wherein the combined fuel flow of the atomizer nozzle manifold and lower air blast nozzle manifold substantially equals that of the upper air blast nozzle manifold.
 21. The improvement of claim 20, wherein the head effect valve communicates with both fuel pressure being supplied to the atomizer nozzle manifold and fuel pressure being supplied to the lower air blast nozzle manifold.
 22. The improvement of claim 21, wherein the head effect valve includes a valve member, a load member, and a pin.
 23. The improvement of claim 16, wherein the first splitter valve provides a low volume fuel flow path to the second splitter valve during engine start-up and a second high volume fuel flow path to the second splitter valve during engine running conditions.
 24. The improvement of claim 23, wherein the first splitter valve provides a different rate of fuel flow to the atomizer nozzle manifold during engine running conditions so that the different rate of fuel flow to nozzles of the atomizer nozzle manifold is substantially equal to the rate of fuel flow to an air blast nozzle in the lower air blast nozzle manifold.
 25. An ecology valve for withdrawing fuel from a plurality of discrete engine fuel manifolds during cessation of engine operation and for returning fuel to at least one of the engine fuel manifolds to be burned during engine operation comprising: a valve housing including at least two ports adapted to be coupled to corresponding ones of the engine fuel manifolds, and a control port adapted to be connected to a corresponding control port of a fuel pressurizing valve; and a movable piston supported within the valve housing for reciprocable motion along an axis, the piston dividing the valve housing into a variable volume control chamber coupled to the control port and a variable volume fuel reservoir, piston motion opening and closing selectively at least two ports, the piston having one extreme position in which a first of the two ports is open to couple the fuel reservoir to a first engine fuel manifold while the remaining one of said at least two ports is closed isolating the reservoir from the remaining engine fuel manifold, and a second extreme position in which a second of said two ports is open to couple the fuel reservoir to a second engine fuel manifold while the first of said two ports is closed isolating the reservoir from the first engine fuel manifold.
 26. The ecology valve of claim 25, wherein there are three ports opened and closed selectively by piston motion, the third port opening to couple the fuel reservoir to a third engine fuel manifold only while the piston closes both the first and second ports.
 27. An ecology valve for withdrawing fuel from a plurality of discrete engine fuel manifolds during cessation of engine operation and for returning fuel to at least one of the engine fuel manifolds to be burned during engine operation comprising: a valve housing including a plurality of ecology ports adapted to be coupled to corresponding ones of the engine fuel manifolds, and a control port adapted to be connected to a corresponding control port of a fuel pressurizing valve; and a movable piston supported within the valve housing for reciprocable motion along an axis, the piston dividing the valve housing into a variable volume control chamber coupled to the control port and a variable volume fuel reservoir uncoupled selectively from the ecology ports by the piston, the piston having one extreme position in which the piston closes at least a first ecology port and a second extreme position in which the piston closes at least a second ecology port.
 28. The ecology valve of claim 27, wherein there are three ecology ports which are never simultaneously open and fuel is withdrawn from the several manifolds seriatim.
 29. The ecology valve of claim 27, wherein the piston is movable through a sequence of nonoverlapping ranges and opens one port in each range whereby withdrawing from or supplying fuel to any one manifold is substantially completed before the withdrawing from or supplying to another manifold commences.
 30. The process of operating an engine of the type having a plurality of fuel manifolds from an engine-off condition, through start-up and engine run, shut-down and back to the engine-off condition, comprising: discharging a quantity of fuel from an ecology reservoir into at least one manifold; supplying a quantity of additional fuel from a fuel source to at least one manifold to initiate engine start-up; increasing the supply of fuel to all manifolds to bring the engine to engine run operation; interrupting fuel flow to all the manifolds to initiate engine shut-down; sequentially extracting fuel from the manifolds and storing the extracted fuel in the ecology reservoir to be burned during a subsequent engine start-up.
 31. The process of claim 30, wherein there are three manifolds and three disjoint time intervals, one for each manifold, during which fuel is extracted from a respective manifold.
 32. A fuel control system for supplying metered quantities of fuel to a plurality of engine fuel manifolds which include an atomizer nozzle manifold, a lower air blast nozzle manifold and an upper air blast nozzle manifold, the improvement comprising: a fuel flow restricting valve which comprises a valve member, means for exerting a load upon the valve member, and a pin member, the fuel flow restricting valve communicating with both fuel pressure being supplied to the atomizer nozzle manifold and fuel pressure being supplied to the lower air blast nozzle manifold, whereby the fuel flow restricting valve reduces fuel flow to the air blast nozzles of the lower air blast nozzle manifold in order to compensate for greater fuel flow to the atomizer nozzle manifold during engine start-up conditions, and the combined fuel flow of the atomizer nozzle manifold and lower air blast nozzle manifold substantially equals that of the upper air blast nozzle manifold during both engine start-up and running conditions.
 33. The fuel control system in accordance with claim 32, further comprising a first splitter valve distributing fuel flow between the atomizer nozzle manifold and the reamining manifolds, and a second splitter valve down stream from the first splitter valve and distributing fuel flow between the upper and lower air blast nozzle manifolds.
 34. The improvement of claim 33, wherein the second splitter valve provides a pair of low volume fuel flow paths to the upper and lower air blast nozzle manifolds during engine start-up and a second pair of high volume fuel flow paths to the upper and lower air blast nozzle manifolds during engine running conditions.
 35. A fuel control system including a pressurizing valve and for supplying metered quantities of fuel to a plurality of engine fuel manifolds which comprise an atomizer nozzle manifold, a lower air blast nozzle manifold and an upper air blast nozzle manifold, the improvement comprising: fuel flow dividing means intermediate the pressurizing valve and the engine fuel manifolds for appropriately distributing fuel flow among the plurality of engine fuel manifolds, the dividing means including first passage means for fuel flow directly to the atomizer nozzle manifold during engine start-up, second passage means for receiving fuel flow directed also to the lower air blast nozzle manifold during engine run conditions and restricting the received amount of fuel that flows to the atomizer nozzle manifold, whereby the fuel flow dividing means responds sequentially to increased fuel pressure to effect via the first passage means distribution of fuel to the atomizer nozzle manifold during engine start-up and then for engine run conditions, via the second passage means permitting increased fuel flow for the upper and lower air blast nozzle manfolds while effecting a lesser rate of fuel flow to the atomizer nozzle manifold, such that fuel flow to the nozzles of the manifolds is substantially equal during engine run conditions.
 36. The fuel control system in accordance with claim 35, wherein a fuel control system for supplying metered quantities of fuel from a fuel supply, through a fuel pump, a metering valve and a pressurizing valve to a plurality of engine fuel manifolds including an atomizer nozzle manifold, an upper air blast nozzle manifold and a lower air blast nozzle manifold, an improved fuel flow dividing arrangement intermediate the pressurizing valve and the engine fuel manifolds for appropriately distributing fuel flow among the plurality of engine fuel manifolds comprising: a concatenated pair of two-way splitter valves comprising a first splitter valve distributing the fuel flow between the atomizer nozzle manifold and the remaining air blast manifolds, and a second splitter valve distributing the down stream fuel flow from the first splitter valve between the upper and lower nozzle manifolds.
 37. The fuel control system in accordance with claim 36, further comprising a fuel flow splitter valve downstream the fuel flow dividing means and distributing fuel flow between the upper and lower air blast nozzle manifolds. 